There are three types of color receptors in our eyes,
red, green and blue. We also have black and white receptors. They are more sensitive than
the color receptors, that is why we have poor color
perception in the dark.

Color blindness comes as a result of a lack of one or
more of the types of color receptors. Most color perception defects are for red or green
or both. About 10% of males have a color perception defect, but this is rare in females.
Red-green color blindness is a result of a lack of red receptors.

Another form of color blindness -- yellow-blue is the
second most common form, but it's extremely rare. It is also possible to have the color
receptors missing entirely, which would result in black and white vision.